The long term objective of this research is to elucidate the molecular mechanisms and developmental consequences of cell-cell fusion events. Sperm-egg fusion is used as a model. Fertilin alpha and beta are sperm surface proteins involved in binding and fusion to the egg plasma membrane. They ar also prototypes of the ADAMs, a novel family of cell- interactive proteins. Fertilin beta contains an integrin ligand domain of the disintegrin motif; fertilin a contains a candidate fusion peptide similar to those found in viral fusion proteins. The egg integrin alpha6beta1 is involved in sperm binding. These findings suggest two major hypotheses: (a) The fertilin a/b complex is involved in alpha-6-beta-1-mediated adhesion, fusion, and signal transduction with the egg--hence the activation of zygotic development. (b) Other ADAMs use similar strategies for adhesion, fusion, and signal transduction. The major goals of this proposal are to test these hypotheses. The specific aims are to: 1. demonstrate and characterize the interaction between the disintegrin domain of fertilin beta and alpha-6-beta-1; 2. demonstrate that fertilin alpha possesses bona fide membrane fusion activity; and 3. characterize the signals transduced when the disintegrin domain of fertilin beta binds to 6-beta-1. The experimental design is modeled on previous studies of viral adhesion/fusion proteins, integrins, disintegrins, and integrin-mediated signal transduction. It employs a combination of biochemical, cell and molecular biological approaches. In addition to its relevance to the basic cell biological process of cell-cell adhesion, cell-cell fusion, and adhesion/fusion-mediated signal transduction, the project has a high degree of health relatedness. Peptide analogs of disintegrins block platelet aggregation and are being explored as anticoagulants. Peptide analogs of the fertilin disintegrin domain block fertilization in vitro. Hence the project should lead to the development of novel contraceptive agents; it may also shed light on the etiology of certain forms of infertility. The project should also provide insights into pathologies that may involve other ADAMs, for examples metastasis and certain developmental abnormalities.